The objective of this application is to compare the clinical effectiveness and the cost-effectiveness of CT colonography (CTC) to optical colonoscopy (OC) in the detection of colon polyps and cancers in the post- resection surveillance setting. There are more than 1,000,000 survivors of colorectal cancer (CRC) in the US with approximately 150,000 new cases annually. Nearly all are eligible to participate in well accepted post- operative surveillance strategies. Clinical guidelines advocate annual abdominal/pelvic CT scan and OC one year after surgery and then every three years. Recently, CTC which combines CT imaging of abdomino-pelvic contents with intra-luminal colonic imaging has garnered attention as an option for routine CRC screening. We hypothesize it may also prove a cost-effective, clinically useful substitute for independent CT scan and OC as a surveillance technique. In our study, CRC patients (n=1000) from the Fox Chase Cancer Center, University of Wisconsin and the Mayo Clinic (Rochester), one year removed from curative resection, who have completed other cancer therapy, will undergo CTC examination with same day OC to follow. Participants will also provide questionnaire responses regarding preferences about CTC vs. separate imaging and endoscopic procedures. The study has three Specific Aims: 1. To evaluate the test characteristics (sensitivity, specificity, positive and negative predictive value) of CT colonography (CTC) for detecting colorectal adenomas and cancers in the post-resection surveillance setting, using optical colonoscopy (OC) as the reference standard. 2. To compare the costs and outcomes, from the payor's and society's perspectives, of CTC versus independent OC plus CT for post-resection surveillance, using standard methods of cost-effectiveness analysis. 3. To assess patient preference for CTC versus separate radiologic and endoscopic evaluation in the post-resection surveillance setting. Approximately 48 months of enrollment is anticipated. Adequate statistical power will exist to demonstrate that the sensitivity and specificity of CTC are not significantly less than 90% relative to OC. In addition, we will generate cost-effectiveness models from the payor and societal perspectives investigating the role of CTC in post-operative surveillance. Data management and analysis will be completed at Fox Chase. An important, but largely unstudied, potential role for CTC is as a component of post-operative surveillance. If CTC is found to be a safe, clinically similar alternative to OC, but more cost-effective and/or preferred by patients, this would provide evidence based support for incorporation of CTC in surveillance recommendations after potentially curative CRC surgery.